(Meth)acrylic esters have been used in various applications as raw materials of paints, adhesives, tackifiers, synthetic resins, fibers or the like. The (meth)acrylic esters have been generally produced by the method of subjecting (meth)acrylic acid and alcohol to esterification reaction in the presence of an acid catalyst.
The (meth)acrylic acid used in the esterification reaction have been usually produced by subjecting propylene to gas-phase oxidation reaction and dehydration reaction, and then purifying the resultant product to remove low-boiling impurities and high-boiling impurities therefrom. There have been proposed industrially advantageous methods in which acrylic acid is purified at low costs by omitting the step of removing high-boiling impurities (for example, Japanese Patent Application Laid-open (KOKAI) Nos. 9-157213, 10-237012, 10-306052 and 2001-213839).
However, in the case where the acrylic acid still containing high-boiling impurities which is obtained by the above methods is subjected to esterification reaction, the following problems are caused. That is, the acrylic acid contains, in addition to the high-boiling impurities, transition metal components derived from a polymerization inhibitor used in the step of purifying the acrylic acid. When the acrylic acid containing such transition metal components is subjected to the esterification reaction, an esterification reaction catalyst used therein tends to be significantly influenced by the transition metal components. For example, in the case where the esterification reaction catalyst is in the form of a solid acid catalyst, the transition metal components tend to be absorbed on active sites of the catalyst, resulting in deactivation of the catalyst. Further, in the case of organic acid catalysts, the transition metal components are reacted with the organic acid to form a complex therewith and, therefore, then insolubilized and precipitated, resulting in occurrence of clogging in conduits as well as failure to continue a stable operation for long period of time.
On the other hand, even when the above acrylic acid containing the high-boiling impurities is purified using high-boiling impurity separation column, the purified acrylic acid distilled off from a top of the high-boiling impurity separation column tends to contain the transition metal components owing to entrainment of splash upon the distillation. Therefore, even though such a purified acrylic acid is subjected to the esterification reaction, the esterification reaction catalyst also tends to suffer from the same significant problems as described above.